This project is concerned with the capacity of human subjects to adapt to a regimen of slowly inrementing sleep restriction. Folloing a two month ad lib sleep period, sleep will be gradually restricted until decrements appear on clinical neuromedical examination, objective performance tests or until subjects no longer maintain a sense of well being. Sleep will be recorded every third night from the subjects' homes and scored into conventional sleep stages. Up to 7 hours ad lib sleep will also occasionally be recorded. Performance and contingent negative variation will also be measured periodically. Self-rating of affect will occur every third night. Periodic ratings of fatigue recorded during the day will be obtained. Following the sleep restriction, subjects will continue for two months at the maximal level of restriction consonant with adaptation. Sleep restriction will be maintained for an additional six months with occasional elctrophysiological recordings. Eight adult subjects, carefully selected from graduate students, will be studied. The significance of the research is in relation to increasing understanding of sleep restriction using a gradual deprivation approach, which has not been attempted previously.